Preforms made out of a thermoelastic material, for instance PET, are used for the production of plastic bottles. The preforms are first warmed or heated and than blow moulded into the desired form in a stretch blow or blow moulding device. The preforms are especially transported on conveying means through a heating device before being processed in the blowing station.
During the currently used process the preforms are held in the heating device by a shaft that is located on a rotary bearing on a link of a transport chain. In a heating device a plurality of chain links with pivoted shafts are connected to form an endless circumferential transport chain. On the outer side of the straight side walls of the oven heating means are arranged, especially IR emitters, that apply the required heat onto the preforms. On the inner side and at the bottom reflectors are arranged to make the best use of the IR radiation. Air is blown into the oven through slots in the reflectors arranged opposite the heating means to cool the surface of the preforms preventing burns on the preform surface mantle area.
Because of continually rising energy prices a high efficiency of the machinery and the facilities achieves more and more importance. It is known that a constriction of the heating tunnel improves the efficiency of the energy use during the heating process.
A major disadvantage when narrowing the heating tunnel is that the IR emitters are closer to each other which leads to a dramatic increase in the temperature of the emitter bulbs. The temperatures can rise as high as 900° C. and/or even higher. This leads to premature failure of the bulbs and to reduced lifetimes. Therefore the emitters need to be cooled.
DE 20 020 150 U1 describes a heating path for stretch blow moulding of preforms with IR emitters, whereby the reflector arranged opposite the emitters has cooling surfaces and/or is actively cooled.
DE 35 10 241 A1 shows a heating device whereby a fan is blowing cool air to the connections and back sides if the IR emitters to cool them down thereby elongating their lifetime.
DE 600 30 327 T2 shows IR emitters that are cooled by an air flow. The air flow first meets the surface of the preforms. After that the air flow is directed to the emitters and their sockets through suitable openings.